Chloroprene polymers containing benzylthiourea accelerators



United States Patent lice Patented Nov. 3, 1959 CHLOROPRENE POLYMERS CONTAI NTN G' BENZYLTHIOUREA ACCELERATORS Lester A. Brooks, East Norwallr, and Jack C. Bacon, Noroton Heights, Conn., assignors to R. T. Vanderbilt Company, Inc., New York, N.Y., a corporation of New York No Drawing. Application June 15, 1956 Serial No. 591,518

20 Claims. (Cl. 260-795) Thepresent invention relates to the vulcanization of chloroprene polymers containing novel accelerators and especially to the vulcanization of the chloroprene polymer known as Neoprene type W.

Chloroprene polymers or neoprene are polymers of 2- chloro-l,3-butadiene (chloroprene) and copolymers of chloroprene with dienes or vinyl compounds in which chloroprene comprises the predominant monomer. These polymers or copolymers are usually made in aqueous. emulsions and are available to the rubber trade under such names as. GR-M, Neoprene type GN, Neoprene type GNA, Neoprene type FR, Neoprene type E, Neoprene type K, Neoprene type KNR, Neoprene type W, and Neoprene type WRT. The various types of polychloroprene or neoprene differ one from the other in the modifier used in controlling the degree of polymerization of chloroprene, typical modifiers being sulfur, sulfur di oxide, hydrogen sulfide, 'mercaptans, iodine compounds, and aromatic azo compounds. The chloroprene polymer which has found wide commercial acceptance because of its uniformity in jmolecular weight distribution and useful properties is'Neoprene type W, a stabilized chloroprene polymer containing no sulfur, thiuram disulficle, or other compound capable of decomposing to liberate free sulfur or form vulcanization accelerators.

Polychloroprenes difier greatly from other synthetic rubbers and from natural rubber in the manner in which they can be vulcanized. canizates may be obtained from polychloroprenes by incorporating certain metallic oxides, such as zinc oxide and magnesia, into the plastic chloroprene and heating to efiect vulcanization. For certain applications litharge is recommended for use in place of the zinc oxide and magnesia, while" in some types sulfur is recommended but is not necessary to effect vulcanization. v

When a more rapid rate of cure is desired than is alforded by the metallic oxides alone, it has been the In general, excellent vulcustom of the rubber trade to employ certain organic compounds as accelerators in conjunction with these metallic oxides. Thiocarbanilide or N,N-diphenylthio urea is an example of an accelerator'which has been used heretofore in the vulcanization of natural rubber, while catechol and hexamethylenetetramine are examples of previously used accelerators in the vulcanization of polychloroprene. The accelerator which has proved most effective in the vulcanization of polychloroprene, however, is ethylenethiourea. However, these accelerators as well as others all suffer from certain defects in that the vulcanizates do not have the desired properties. For example, the tensile strength of vulcanizates cured in the presence of thiocarbanilide is not as high as might be desired. In addition, accelerators such as ethylenethiourea are scorchy, i.e., they are so active at relatively low temperatures that the polychloroprene is liable to cure prematurely, or scorch, during processing and accordingly cause economic losses. Furthermore, polychloroprene vulcanizates cured in the presence of ethylenethiourea do not have as high elongation values as is desired. r 7

Accordingly, it is the object of the present invention to provide a novel group of accelerators for the vulcanization of chloroprene polymers and especially for the vulcanization of Neoprene type W which 'will impart to the vulcanizates the desired physical properties and scorch'values.

The accelerators of the presentinvention are thiourea accelerators having the general'formula Where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms. Accordingly, it will be appreciated that R R R and R may be the same or difierent and that the alkyl radicals may be straight or branch chain radicals. Typical examples of the accelerators includeN,N-di-alpha-methylbenylthiourca, N,N dibenzylthiourea, N-alpha-methylbenzyl N-benzylthiourea, N-alpha-phenylpropyl-N-alpha phenylamylthiourea, N- alpha phenyl alpha methylethyl N alpha phenyl-alpha-ethyl-propylthiourea, and N-alpha-methyl-benz-' yl-Nwalpha-phenyl-alpha-propyl amylthiourea.

These thiourea accelerators may be prepared by classical methods. One such method of preparation involves the reaction of a primary amine with carbon disulfide to form the amine salt which is then heated to drive off hydrogen sulfide, sometimes expedited in the presence of traces of acid. This reaction may be illustrated as follows:

R u heat 1| 2RNH, OS, RHNosNH, 3g RHNCNHR In the above equation R represents a benzyl radical or alpha-substituted benzyl radicals wherein the substituents are alkyl radicals having from one to five carbon atoms. A specific illustration of this process involving the preparation of N,N'-dibenzylthiourea is as follows:

' thiocyanates, Where the alpha substituents are alkyl radi cals having from one to five carbon atoms. Further details as to these methods of preparation as Well as others may be readily obtained by reference to the article titled Thioureas appearing in Chemical Reviews, volume 55, pages l81'228 (1955), by Dorothy C. Schroeder. p g

The amount of the thiourea accelerator which may be employed in the vulcanization of chloroprene polymers may vary within rather broad limits. In general, from about 0.05% to about 5.0% of the thiourea accelerator based on the weight of the chloroprene polymer is employed. It is preferred to use from about 0.5% to about'l.()% of the thiourea accelerator based on the weight of the chloroprene polymer present in the stock to be vulcanized.

The'accelerators may be used in conjunction with theconventional ingredients used in compounding polychloroprene articles. Such ingredients include, for ex-- ample, antioxidants, fillers, colors, metallic oxides, sof- V teners, and the like.

The invention will be further illustrated by the data presented below in connection with Table I.

A typical polychloroprene, namely Neoprene type W,

was compounded by milling together the ingredients in the following base formula:

Parts by weight In the above formulation Agerite Stalite is a proprietary antioxidant composition composed of octylated diphenylamines and P-33 Black is a proprietary composition of fine thermal carbon black. This polychloroprene stock was vulcanized by air curing at 307 F. for varying lengths of time as shown in Table I below. After curing, the vulcanizate was tested for Mooney scorch, stress, tensile strength, elongation, and hardness. Typical thiourea accelerators of the invention were compared with heretofore known accelerators, namely thiocarbanilide and ethylenethiourea. In Table I below the accelerators designated by the numbers 1 through 3 were respectively (1) N,N-di-alpha-methylbenzylthiourea, (2) N,N-dibenzylthiourea, and (3) N-alpha-mcthylbenzyl- N'-benzylthiourea.

Table I Thio- Ethyl- Accelerator 1 2 3 carban-enethio- I llide urea Mooney Scorch at 250 F. (6 point rise) Stress in P.s.i. at 300% Elongation Air Cure in Minutes at Tensile Strength in P.s.i.

Percent Elongation at Break Shore Hardness No.

From a study of the data presented above in Table I y it may be readily seen that the novel thiourea accelerators all eifect a cure of a polychloroprene elastomer. The novel thiourea accelerators impart physical properties to the vulcanizates which are comparable to those imparted thereto by ethylenethiourea or superior thereto, e.g., higher elongation, and in addition the accelerators of the invention are far less scorchy than is ethylenethiourea as shown by the higher Mooney scorch values. Also, the accelerators of the invention impart to polychloroprene vulcanizates physical properties comparable to or better than those imparted to vulcanizates by thiocarbanilide. In particular, the polychloroprene vulcanizates formed in the presence of the accelerators of the invention have a higher tensile strength than do the vulcanizates containing thiocarbanilide. It will be appreciated that other accelerators of the invention may also be employed with comparable results and that the thiourea accelerators may be employed with chloroprene polymers other than Neoprene type W.

Various modifications and changes may be made in the invention herein set forth without departing from the spirit thereof and accordingly the invention is to be limited only within the scope of the appended claims.

We claim:

1. A vulcanizable polychloroprene composition comprising an unvulcanized chloroprene polymer and from about 0.05% to about 5.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula e 5 CH5 HNCNH I GoHa where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms.

2. A vulcanizable polychloroprene composition comprising an unvulcanized chloroprene polymer and from 0.5% to about 1.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula where R R R and R are radicals selected from the benzylthiourea.

6. A vulcanizable polychloroprene composition comprising sulfur free polychloroprene and from about 0.05% to about 5.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms.

7. A vulcanizable polychloroprene composition comprising sulfur free polychloroprene and from about 0.5% to about 1.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula R, i R, o mf tnNcNH+otm R1 R;

where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms.

8. A composition as set forth in claim 7 wherein the thiourea compound is N,N'-di-alpha-methylbenzy1- thiourea.

9. A composition as set forth in claim 7 wherein the thiourea compound is N,N-dibenzylthiourea.

10. A composition as set forth in claim 7 wherein the thiourea compound is Nalpha-methylbenzyl-N'- benzylthiourea.

11. The process of vulcanizing chloroprene polymers comprising incorporating in a chloroprene polymer stock from about 0.05% to about 5.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms, and heating at vulcanizing temperatures to cure the polymer.

12. The process of vulcanizing chloroprene polymers comprising incorporating in a chloroprene polymer stock from about 0.5% to about 1.0% of the Weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms, and heating at vulcanizing temperatures to cure the polymer.

13. The process as set forth in claim 12 wherein the thiourea compound is N,N'-di-alpha-methylbenzylthiourea.

14. The process as set forth in claim 12 wherein the thiourea compound is N,N'-dibenzylthiourea.

15. The process as set forth in claim 12 wherein the thiourea compound is N-alpha-methylbenzyl-N'- benzylthiourea.

16. The process of vulcanizing chloroprene polymers comprising incorporating in sulfur free polychloroprene stock from about 0.05% to about 5.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula Where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms, and heating at vulcanizing temperatures to cure the polymer.

17. The process of vulcanizing chloroprene polymers comprising incorporating in sulfur free polychloroprene stock from about 0.5 to about 1.0% of the weight of the polymer of a thiourea compound capable of acting by itself as a vulcanization accelerator for the polymer and having the general formula .Ri S

o H oHNi N a 5 l E 0511 1 15: IL; where R R R and R are radicals selected from the group consisting of hydrogen and alkyl radicals having from one to five carbon atoms, and heating at vulcanizing temperatures to cure the polymer.

18. The process as set forth in claim 17 wherein the thiourea compound is N,N'-di-alpha-methylbenzylthiourea.

19. The process as set forth in claim 17 wherein the thiourea compound is N,N-dibenzylthiourea.

20. The process as set forth in claim 17 wherein vthe thiourea compound is N-alpha-methylbenzyl-N- benzylthiourea.

References Cited in the file of this patent UNITED STATES PATENTS 2,071,966 Bolton Feb. 23, 1937 2,397,399 Baird Mar. 26, 1946 2,544,746 Baum Mar. 13, 1951 2,804,447 Naylor Aug. 27, 1957 OTHER REFERENCES Dehn: J. Am. Chem. Soc., 62, 3189, 3130 (November 1940).

UNITED STATES PATENT OFFICE CERTIFICATE or ECTU Patent No 2,911,394 November 3, 1959 Lester Ao Brooks et air It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 44, list of references cited, under "OTHER REFERENCES", for "3130 read 3190 Signed and sealed this 10th day of May 1960,

(SEAL) Attest:

KARL TL AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. A VULCANIZABLE POLYCHLOROPRENE COMPOSITION COMPRISING AN UNVULCANIZED CHLOROPRENE POLYMER AND FROM ABOUT 0.05% TO ABOUT 5.0% OF THE WEIGHT OF THE POLYMER OF A THIOUREA COMPOUND CAPABLE OF ACTING BY ITSELF AS A VULCANIZATION ACCELERATOR FOR THE POLYMER AND HAVING THE GENERAL FORMULA 